Structure‐dependent relative toxic potencies of selected pyrrolizidine alkaloids

Pyrrolizidine alkaloids are naturally occurring secondary plant metabolites mainly found in families of Asteraceae, Boraginaceae, and Fabaceae. Chemically, Pas consist a pyrrolizidine core bearing hydroxyl groups, the so-called necine base, mono- or dicarboxylic acids bound to via ester linkages. 1,2-unsaturated PAs hepatotoxic, genotoxic, carcinogenic due highly reactive pyrrolic formed by cytochrome P450 monooxygenases (CYPs) primarily liver. The presence as frequent contaminants wide variety food feed products has be considered relevant safety issue. Based on currently available data, risk assessment was approached using two most toxic potent congeners, i.e., lasiocarpine riddelliine. However, it is well recognized that toxicity differing significantly between congeners related their structural features. PA-containing indeed overestimated, comprehensive should take these differences into account. After analyzing data many PAs, Merz Schrenk derived interim Relative Potency (iREP) factors present sub-groups PA concerning use such iREP could probably provide more scientific basis for until sufficient experimental analysis toxicities individual applied. To obtain better understanding relationship structure evidence further refinement relative (toxic) potency factors, vitro cytotoxicity, genotoxicity, mutagenicity diverse (lasiocarpine, monocrotalineφ, retrorsine, senecionine, seneciphyllineφ, echimidineφ, europineφ, heliotrineφ, indicine, lycopsamine) been generated our project supported Kooperation Phytopharmaka. Among them, lasiocarpine, indicine lycopsamine have investigated my part. Cytotoxicity assessed Alamar blue assay primary rat hepatocytes, HepG2 cells, (CYP3A4) cell line. In none selected exhibited cytotoxic effects, lack CYPs. hepatocytes HepG2(CYP3A4) clear dependent cytotoxicity demonstrated. role CYP450 enzymes metabolic activation confirmed an inhibition assay. A kinetic 7-benzyloxyresorufin-O- dealkylation (BROD) used measuring activity enzymes. Furthermore, utilization glutathione-reductase-DTNB recycling indicated glutathione might not play critical PA-induced cytotoxicity. micronucleus test determining clastogenic genotoxicity. All concentration-dependent cells. potencies estimated from generally consistent with following ranking: > senecionine seneciphylline retrorsine heliotrine (?) echimidine europine = monocrotaline. evaluated based findings were completely classification previously reported Schrenk. Monocrotaline both assays considerably lower potency. Echimidine, however, than expected. On other hand, measured Ames fluctuation Salmonella typhimurium strains TA98 TA100. None up 300 μM showed mutagenic effects despite S9-mix.